Evidence for disequilibrium of ortho and para hydrogen on Jupiter from Voyager IRIS measurements

Abstract

Specification of the ratio of molecular hydrogen in the ortho state (parallel proton spins) to that in the para state (antiparallel proton spins) has long been a problem encountered in the modelling of the atmospheres of the outer planets^1–3. At deeper atmospheric levels where the temperature exceeds 300 K, a ‘normal’ ortho–para ratio of 3:1 will exist; as a parcel is transported upwards to cooler levels, the ratio can either remain fixed or move toward the ‘equilibrium’ value at the local temperature, depending on the relative magnitudes of the equilibration and transport times, neither of which is well known. To make further progress in the investigation of these processes, it is important to determine the ortho–para ratios within the observable portions of the atmospheres of the giant planets. Here we present preliminary results of an analysis of the H₂ ortho–para ratio in the atmosphere of Jupiter using Voyager infrared spectrometer (IRIS) data.